1. Field of the Invention
The present invention relates generally to surgical apparatus and more particulary to a milling tool for the preparation of a joint socket in total prosthesis of a joint.
2 Prior Art
In the total prosthesis of joints such as a hip joint, the existing hip joint ball is removed and the hip joint socket is shaped and enlarged to receive a pre-formed artificial hip joint ball or a pre-formed artificial socket which will matingly engage an artificial hip joint ball. Proper seating of the artificial ball in the pathologically altered hip joint socket is dependent on the careful and accurate preparation of the socket.
While a hammer and chisel were the principal tools used to prepare the hip socket in early prosthesis procedures, these instruments have largely been replaced by milling tools. Milling tools reduce the time required to prepare a hip socket and facilitate the accurate shaping of the socket.
One proposed milling tool has a hemispherical tool body which is of solid construction. Milling blades of quarter-circle shape are provided on the body in a spiral arrangement. In a second proposed milling tool, several radially arranged plates form a generally hemispherically-shaped tool body. Milling blades are formed on the edges of the plates. Neither of these milling tool structures is well adapted for use in milling the several types of tissues encountered in a joint socket such as connective fatty tissues, joint cartilage, and bone tissues of differing densities. In the first proposed construction, the channels between the milling blades tend to stop up easily, while in the latter proposed construction a danger exists of breaking into aged de-limed bones.
A third proposal which represents an improvement over the described milling tools utilizes a hollow hemispherical tool body. Milling blades are formed on the body as by forming openings through the body and by sharpening selected edges of these openings. This proposed tool has been found to be acceptable for safely and expediently milling all forms of joint tissue.
A problem with all three of these proposed tools is that milled tissue material is not thoroughly collected by the tool and tends to collect in the softer tissues of the joint during milling. The milled tissue particles are not easily removed from the wound surface even with the most thorough rinsing and swabbing procedures.
Tests have shown that where ossifications have resulted in the immediate vicinity of an artificial joint, the milling residues which are left in the joint are a significant factor in their causation. Such ossifications can lead to a limitation in joint movement and even to a complete stiffening of the joint.